1. Field of the Invention
The present invention relates to a discharge lamp lighting device.
2. Description of the Prior Art
Heretofore, there have been proposed many different discharge lamp lighting devices; generally, they comprise, in order to effectively light the discharge lamp, a power circuit which supplies a constant current or power corresponding to the rating of an object discharge lamp, a starter which applies a high voltage pulse to cause a dielectric break-down in the discharge lamp in order to start lighting the lamp, and a boost voltage supplying circuit to provide a boost voltage which facilitates the discharge lamp to transfer to a stable discharge state at earlier stage of lighting.
Said starter is automatically actuated when the power circuit and the boost voltage supplying circuit have completed the preparatory operation, and also automatically stopped when the discharge lamp is lighted; the starter should preferably be controlled in this way.
FIG. 1 shows an explanatory circuit diagram of a conventional discharge lamp lighting device with such functions. In this example, between the output terminals of the power circuit 2 connected to an A.C. power source 1 connected is a boost voltage charging capacitor C1 across which is connected to a boost voltage generator circuit 3. The above components form together a ballast 4. The power circuit 2 comprises a transformer, rectifier, and filter circuit. If a filter capacitor for the filter circuit also serves as the boost voltage charging capacitor, the boost voltage generator circuit may be connected across the filter capacitor. The discharge lamp L is connected by means of a starter 5 to the output terminal of the ballast 4, more particularly across the capacitor C1. The starter 5 is formed by connecting the primary coil of a commercial high voltage transformer T1 to a commercial power source 6 through a normally open relay contact ry of a relay RY inserted in parallel with said capacitor C1, and connecting the primary coil of a Telsa coil TC to the secondary coil of said transformer T1 by means of a starting capacitor C2 and discharge gap G, and interposing the secondary coil of the Tesla coil TC between said capacitor C1 and discharge lamp L.
The discharge lamp lighting device of such construction functions as follows: When the ballast 4 is actuated, the capacitor C1 is charged with boost voltage from the boost voltage generator circuit 3, and the voltage V.sub.C across the capacitor increases to reach a boost voltage V.sub.A of a required amplitude, as shown in FIG. 2(A). Then, at the time T.sub.1, the relay RY is energized with said boost voltage V.sub.A so that the normally open relay contact ry is closed. An A.C. voltage from the commercial A.C. power source 6 is applied to the commercial high voltage transformer T1, as shown in FIG. 2(B). The high voltage current induced in the secondary coil of the transformer T1 flows to the primary coil of the Tesla coil TC so that high voltage pulses are induced in the secondary coil of the Tesla coil TC, as shown in FIG. 2(C). The high voltage pulses are applied to the discharge lamp L where dielectric break-down occurs to start discharging. When the lamp L is lighted, the voltage V.sub.C across the capacitor C1 drops to the rated voltage so that the relay RY is deenergized. Then, the normally open contact ry thereof is opened with the result that the generation of high voltage pulses from the Tesla coil TC is suspended. More particularly, when the ballast 4 is ready for lighting the discharge lamp L, the starter 5 is actuated, and when the discharge lamp L is lighted, it is stopped. This operation is automatically done by setting the relay actuating voltage to the boost voltage V.sub.A.
However, in such conventional discharge lamp lighting device, since the commercial power source 6 is used as power source to energize the starter 5 in addition to the power source 1 for the power circuit 2, the entire device has a complicated construction; further, because of the commercial high voltage transformer T1 being used to apply the high voltage at the secondary coil thereof to the Tesla coil TC at the primary coil thereof, said starter 5 consumes much power. In case this starter 5 is adopted in the lighting device for a discharge lamp L such as xenon shortarc lamp of 350 W in rating, for instance, electric energy as large as 100 VA is consumed to light the lamp L.